Miniature motors of the above-referenced type are frequently brushless direct current motors, which are also called BLDC motors (BLDC=brushless direct current). Because of their very small overall size with an outer diameter of only a maximum of 6 mm, the determination of the rotational rotor position, which is required for commutation control, takes place usually without sensors, generally on the basis of a determination and evaluation of the back EMF, that is, a voltage back-induced in the stator coils during rotation. It is thus difficult to realize an actuation at low speeds or even a rotational position regulation with such miniature motors.
On the other hand, in larger motors with a diameter of more than 6 mm, sensors can be used, in particular Hall-effect digital sensors, because the larger overall size allows accommodation of the sensors. The sensors can thus be arranged, for example, eccentrically around the periphery at specific peripheral angle intervals, wherein however an exact position alignment of the individual sensors is required.
EP 0 920 113 B1 describes a brushless direct current motor with a sensor arranged eccentrically radially beside the rotor, wherein the rotor has additionally a special permanently magnetized measuring magnetization zone. DE 10 2007 000 440 A1 also discloses a rotational angle detection device, which is positioned eccentrically radially beside the rotor.
According to EP 0 510 336 B1, the magnetic stray field of the motor magnet is utilized, but only the direction of rotation, not the angular position, is to be detected.
United States patent application 2001/0090633 A1 describes the use of a Hall-effect sensor, which however detects the magnetic field of an additional magnetized transmitting magnet with two poles, which rotates together with the rotor via the motor shaft.
Something similar applies also for a motor actuation according to EP 2 117 103 B1.
Finally, individual sensors for determining the magnetic field of the rotor are also utilized according to EP 1 456 935 B1.
All these known configurations are not suitable for a generic miniature motor of the kind discussed herein due to their extremely small overall size, with an outer diameter that must in any case be smaller than/equal to 6 mm.
The aim of the invention is the creation of a miniature motor of the generic kind described above, in which an improved actuation is achieved, in particular also for a rotational position regulation and/or for low speeds, while retaining its small compact design.
This aim is achieved according to the invention. Advantageous embodiments of the invention are disclosed in the dependent claims and in the following description.
It is accordingly provided according to the invention that a sensor chip in the form of at least one magnetic field sensor is arranged in such a way in an area which is axially adjacent to the front face of the magnetic rotor located within a plane that is vertical to the rotational axis is provided for the purpose of detecting the rotational position of the magnetic rotor. The magnetic field sensor is impinged by the magnetic field of the magnetic rotor in such a way that the magnetic field can be evaluated in order to determine the rotational position of the rotor. The magnetic field, that is, the stray field of the magnetic rotor, can thus be advantageously directly detected and evaluated by means of the invention without any additional transmitter elements, in order to detect the rotational position of the magnetic rotor. The sensor chip preferably includes several, and namely at least three, but preferably four individual magnetic field sensors, in particular Hall-effect sensors, integrated in one component. The positioning and alignment of the magnetic field sensors relative to the magnetic rotor is in this way also possible with great exactness within the very small motor; the standard sensor chip only needs to be mechanically positioned on the stator relative to the magnetic rotor.
The sensor chip can be configured with a very flat design, and in particular as a single chip encoder, which comprises a signal evaluation as IC component, which is such that it directly delivers, in addition to the magnetic field sensors, an absolute and/or incremental rotational position signal for an external electronic control system. In this way, the electronic control system can also be designed, in addition to the actual commutation, for the exact regulation of the rotor position and/or also for the adjustment of low rotor speeds. The actuation of the motor can thus be optimally commutated from a standstill across the entire speed range, which would not be possible by means of a synchronic control or with a sensorless control utilizing the back EMF induced voltage in the stator coils. The actuation of the motor can even take place with sinus commutation due to the available output signals of the preferred single chip encoder, which was not possible until now with this type of small motors.
It is furthermore advantageous if the magnetic field sensors integrated into the sensor chip are arranged in an area that covers the axial projection of the magnetic rotor and in a specific peripheral distribution over a reference circle around the extended rotational axis, wherein the reference circle has a diameter that is located in the area between the diameter of the rotor shaft, which corresponds to the inner diameter of the magnetic rotor, and the outer diameter of the magnetic rotor. It is particularly advantageous if the diameter of the reference circle on which the magnetic field sensors are arranged is located within the outer half of the annular cross section of the magnetic rotor. The sensor chip can furthermore be arranged very close to the magnetic rotor. The sensor chip should be spaced from the adjacent front face of the magnetic rotor via an axial gap, which corresponds to a maximum of 1 to 1.5 times the diameter of the reference circle of the magnetic field sensors. It has been shown that a secure detection of the rotational position of the rotor is possible based only on the magnetic field of the rotor by means of this described configuration and arrangement of the sensor chip, and thus without additional transmitter elements, such as in particular separate transmitter magnets.
The same parts are always provided with the same reference signs in the different figures of the drawings.